Wednesday 22 September 1999 21.19 EDT
First published on Wednesday 22 September 1999 21.19 EDT

The dig began last year in a small way: nothing found. Then in May English Heritage's geophysical team, led by Andrew David, resurveyed the field at Beckhampton, three quarters of a mile west of the famous stone circles at Avebury, Wiltshire. What they found in new soil conditions prompted the archaeologists to expand this summer's plans. But none of us was ready for what happened at the dig, which ended last week. It is one of the great discoveries of prehistoric archaeology.

Mark Gillings of Leicester University, Josh Pollard of the University of Wales, Newport and Dave Wheatley at Southampton University, found three buried megaliths and the sites of three more. There are convincing reasons for believing at least 100 stones once stood there, maybe as many as 200. This newly discovered arrangement weighed more than the entire monument at Stonehenge.

Much of our understanding of ancient Avebury depends on an observant 18th century antiquarian, William Stukeley. He recorded prehistoric monuments being destroyed by local farmers. He described the stone rings (100 megaliths encircle two smaller rings), and the West Kennet Avenue, two parallel rows of megaliths 1.5 miles long that end south east of Avebury at a double stone circle he called the Sanctuary.

Excavations and restorations earlier this century, the last in 1939, proved Stukeley right. He also claimed a second avenue lay to the west. For nearly 300 years archaeologists debated the veracity of this claim. No excavations had been conducted. Recent geophysical work had appeared to bolster the view of 19th century researchers: Stukeley made it up.

Now Gillings, Pollard and Wheatley have proved this Beckhampton Avenue a reality. That such a massive component of an apparently well studied prehistoric ritual complex could have gone unnoticed is surprise enough. "The rediscovery of a major megalithic monument has profound implications for our understanding of the Avebury complex and Neolithic society," says Pollard. But now the questions pour out.

Two stones still stand close to the site of the dig. They are among the largest in Britain, and may be part of a different structure altogether. Avebury rings are surrounded by a huge circular earthwork with four entrances. The known avenues connect with two. If a megalithic avenue could be lost, perhaps there are more. And if that's possible, who knows what else lies out there?

For Gillings, it is proof that there is still room for planned fieldwork at famous ancient monuments. "We've put a couple of thousand volts through the World Heritage Site," he says.

In the same week as the discovery of the Beckhampton Avenue, I was directing a smaller dig at the end of the other avenue, inside the Sanctuary. This was supposedly completely excavated in 1930. Since then, academics have argued about exactly what stood in the dozens of post holes revealed.

Did six timber circles rise together with the two stone rings in a modest version of Stonehenge made partly in wood? Or was there a conical thatched roof over a large circular mausoleum or temple, perhaps built and replaced a number of times in slightly different form?

In February I discovered that diaries kept by the dig foreman, William Young, held much new information, some conflicting with the archaeologist's report. The questions could be resolved only by excavation. We found that a pit described in 1930 as having held a single oak post had been re-dug five times. A tree-size timber was repeatedly removed from the ground and the hole backfilled with chalk, before being re-excavated for the placing of another large post. There would have been no need for this under the protection of a roof. This could only have been a free standing "totem pole".

This changes our conception of the Sanctuary. Instead of a static monument of decaying wood and stones we imagine a place of movement and activity. The business was selecting and felling trees, dragging poles to the site, digging pits, carving posts and hauling them into place: doubtless accompanied by noisy and colourful ceremony.

There are other timber rings of this date in Britain, around four to five thousand years ago, none well understood. Archaeologists have long argued that the sophisticated architecture of Stonehenge is a transformation into stone of techniques developed in wood. Sites like the Sanctuary provided the timber models. We already know that megaliths at Stonehenge were repeatedly moved. What we see today must be a fossil, the static culmination of centuries of activity involving very large numbers of people.

In 1996 when Gillings and Pollard named their project "Negotiating Avebury", it seemed an appropriate description for the difficulty they had raising funds. The interest was in ways of conceiving the monuments, both when they were built and subsequently in the minds of observers and antiquarians. Recent archaeologists had written about how Avebury's creators visualised their landscape, relating the monuments to ideas about property, space and time. "Negotiating Avebury" set out to go one further. They would recreate the physical reality.

In the 1930s, Alexander Keiller, with money from the family marmalade business, bought Avebury. He wanted to restore the stone circles to their former glory. To this end he uprooted trees, rehoused villagers and re-erected long fallen megaliths. It was a remarkable act of antiquarian arrogance.

Modern technology enables a reconstruction project bigger in concept than Keiller's, bereft of the social consequences and at a fraction of the cost. Gillings, Pollard and Wheatley would rebuild Avebury in a computer.

A colleague at Newcastle University, Glyn Goodrick, figured out how to capture 3D images of the Avebury megaliths using tiddlywinks. They stuck coloured counters on the stones at significant contouring points. Then they digitally photographed the stones and recorded the counters three dimensionally. The computer merged the "wire-frame" models with the photographs. The result is an eerily realistic Virtual Reality Modelling Language model of the Avebury landscape.

As you "walk through" this landscape, you view things that no archaeologist has seen. Missing megaliths can be replaced at will - and moved again. Views between different parts of the sites, now obscured by modern buildings, open up. This is, says Wheatley, not just a process of reconstruction.

"We believe that virtual reality techniques should be used in an exploratory way in archaeology," he says, "rather than simply as a tool for reinforcing single, monolithic interpretations."

Negotiating Avebury intends to create several models. They are currently working on the site as it is now. Next they will move onto reconstructions of the monument in the prehistoric past - a task suddenly enlarged by the new discoveries. There is even talk of creating a 3D model of Avebury in the 18th century, using dozens of drawings left by William Stukeley.

It is a blending of old and new that characterises modern archaeology. Updates on the Beckhampton dig appeared on the web. A VRML model of the Sanctuary constructed by Jennifer Garofalini, a Southampton student, can be viewed online, together with my full transcriptions of the excavation records left by Cunnington and Young. Wheatley plans to give people web access to the entire Avebury model.

The scene of activity and thought on a grand scale 4,500 years ago, the Avebury landscape is today alive to the mental processes of digital zapping and intellectual argument. William Stukeley would have been delighted.